DZ Pairs (dz + pair)

Distribution by Scientific Domains

Selected Abstracts

The mechanism of emergenesis

D. T. Lykken
Since each individual produced by the sexual process contains a unique set of genes, very exceptional combinations of genes are unlikely to appear twice even within the same family. E. O. Wilson (1978) The intraclass correlations of monozygotic twins who were separated in infancy and reared apart (MZA twins) provide estimates of trait heritability, and the Minnesota Study of Twins Reared Apart [MISTRA: Bouchard et al. (1990), The sources of human psychological differences: the Minnesota study of twins reared apart, Science 250, 223,228] has demonstrated that MZA pairs are as similar in most respects as MZ pairs reared together. Some polygenic traits,e.g. stature, IQ, harm avoidance, negative emotionality, interest in sports,are polygenic-additive, so pairs of relatives resemble one another on the given trait in proportion to their genetic similarity. But the existence and the intensity of other important psychological traits seem to be emergent properties of gene configurations (or configurations of independent and partially genetic traits) that interact multiplicatively rather than additively. Monozygotic (MZ) twins may be strongly correlated on such emergenic traits, while the similarity of dizygotic (DZ) twins, sibs or parent,offspring pairs may be much less than half that of MZ pairs. Some emergenic traits, although strongly genetic, do not appear to run in families. MISTRA has provided at least two examples of traits for which MZA twins are strongly correlated, and DZA pairs correlate near zero, while DZ pairs reared together (DZTs) are about half as similar as MZTs. These findings suggest that even more traits may be emergenic than those already identified. Studies of adoptees reared together (who are perhaps more common than twins reared apart) may help to identify traits that are emergenic, but that also are influenced by a common rearing environment. [source]

Long-Term Leisure Time Physical Activity and Properties of Bone: A Twin Study,,

Hongqiang Ma
Abstract Effects of physical activity on bone properties, when controlled for genetic effects, are not fully understood. We aimed to study the association between long-term leisure time physical activity (LTPA) and bone properties using twin pairs known to be discordant for leisure time physical activity for at least 30 yr. Volumetric BMD and geometric properties were measured at the tibia shaft and distal end using pQCT in 16 middle-aged (50,74 yr) same-sex twin pairs (seven monozygotic [MZ] and nine dizygotic [DZ] pairs) selected from a population-based cohort. Paired differences between active and inactive co-twins were studied. Active members of MZ twin pairs had larger cortical bone cross-sectional area (intrapair difference: 8%, p = 0.006), thicker cortex (12%, p = 0.003), and greater moment of inertia (Imax, 20%, p = 0.024) at the tibia shaft than their inactive co-twins. At the distal tibia, trabecular BMD (12%, p = 0.050) and compressive strength index (18%, p = 0.038) were also higher in physically active MZ pair members than their inactive co-twins. The trends were similar, but less consistently so, in DZ pairs as in MZ pairs. Our genetically controlled study design shows that LTPA during adulthood strengthens bones in a site-specific manner, that is, the long bone shaft has a thicker cortex, and thus higher bending strength, whereas the distal bone has higher trabecular density and compressive strength. These results suggest that LTPA has a potential causal role in decreasing the long-term risk of osteoporosis and thus preventing osteoporotic fractures. [source]

The Moderating Effect of Religiosity on the Genetic Variance of Problem Alcohol Use

ALCOHOLISM, Issue 9 2010
Tanya M. M. Button
Background:, Previous studies have demonstrated that the heritability of alcohol-related phenotypes depends upon the social background in which it is measured (e.g., urbanicity, marital status, and religiosity). The aim of the current study was to identify whether religiosity moderated the genetic variance of problem alcohol use in men and women at two time points: adolescence and early adulthood. Method:, Participants were 312 male MZ pairs, 379 female MZ pairs, 231 male DZ pairs, 235 female DZ pairs, and 275 opposite sex DZ pairs participating in the University of Colorado Center on Antisocial Drug Dependence. Religiosity was measured using the Value on Religion Scale (Jessor and Jessor, 1977), and problem alcohol use was measured using the Composite International Diagnostic Interview,Substance Abuse Module (Cottler et al., 1989). Data were analyzed using a model-fitting approach to the twin data. Results:, In adolescence, genetic variance of problem alcohol use decreased significantly with increasing levels of religiosity in both men and women, whereas in early adulthood, religiosity did not moderate the genetic variance of problem alcohol use in either men or women. Conclusion:, Religiosity appears to moderate the genetic effects on problem alcohol use during adolescence, but not during early adulthood. The reduced genetic variance for problem alcohol use in adolescence may be the consequence of greater social control in adolescence than in young adulthood. [source]

Genetic and environmental influence on language impairment in 4-year-old same-sex and opposite-sex twins

Essi Viding
Background:, We investigated the aetiology of language impairment in 579 four-year-old twins with low language performance and their co-twins, members of 160 MZ twin pairs, 131 same-sex DZ pairs and 102 opposite-sex DZ pairs. Methods:, Language impairment in 4-year-olds was defined by scores below the 15th percentile on a general factor derived from an extensive language test battery. Language impairment of different degrees of severity was investigated by using multiple cut-offs below the 15th percentile. Results:, DeFries,Fulker extremes analysis indicated that language impairment as measured by the general language scale is under strong genetic influence. In addition, group differences heritability showed an increasing trend (from 38% to 76%) as a function of severity of language impairment. Although more boys are impaired than girls, incorporating opposite-sex DZ pairs into the analysis found neither quantitative nor qualitative differences between boys and girls in genetic and environmental aetiologies. Conclusions:, Language impairment at four years is heritable. This finding replicates previous research on language impairment and extends it by showing that language impairment is heritable in twins selected from a representative community sample. Despite the mean difference between boys and girls, genetic and environmental influences are quantitatively and qualitatively similar for language impairment for boys and girls. For both boys and girls, heritability appears to be greater for more severe language impairment, indicating stronger influence of genes at the lower end of language ability. [source]

A relationship between migraine and biliary tract disorders: findings in two Swedish samples of elderly twins

S. Nilsson
Nilsson S, Edvinsson L, Malmberg B, Johansson B, Linde M. A relationship between migraine and biliary tract disorders: findings in two Swedish samples of elderly twins. Acta Neurol Scand: 2010: 122: 286,294. 2009 The Authors Journal compilation 2009 Blackwell Munksgaard. Objectives,,, To investigate whether there is a relationship between the clinical occurrence of migraine and biliary tract disorders (BTD) and to study whether there is a genetic influence on such an association. Materials and Methods,,, The near lifetime morbidity for migraine and BTD was examined in two Swedish twin-samples: OCTO-Twin (149 MZ and 202 DZ pairs; 234 men, 468 women; 80 years of age or older at inclusion), and the GENDER study (249 unlike-sex DZ-pairs; 70,80 years of age at inclusion). The diagnosis of BTD was established by perusal of medical records from the last twenty years. The diagnosis of migraine was based on iterated questionnaires and personal interviews. Results,,, The odds ratio (OR) of BTD among OCTO-Twin subjects suffering from migraine was 3.5 (1.9,6.7) in monozygotic pairs and 1.7 (1.0,2.9) in dizygotic pairs The corresponding figures among the GENDER unlike-sex DZ-pairs was 2.7 (1.6,4.5). Migraine was associated with female sex and waist circumference. Conclusions,,, There is a relationship between the occurrence of migraine and BTD, also when controlling for the fact that both disorders are more frequent in women. The association appears to be partly attributable to genetic influences. [source]